This invention relates to a machine tool that comprises a rotary spindle having a radially movable cutter means on one end thereof. An axially slidable drawbar is arranged within the spindle for moving the cutter means radially into the spindle.
A principal feature of this invention is the mechanism for moving the drawbar axially within the rotating spindle. The mechanism comprises a normally inactive harmonic drive means carried on the spindle, and a cam connection between the output of the harmonic drive means and the drawbar, whereby actuation of the harmonic drive means causes the cam connection to move the drawbar axially. The harmonic drive means is actuated by a brake means that is arranged to engage a reaction member in the harmonic drive means. The brake means can be operated by a remotely-generated electric signal or hydraulic signal.
A principal advantage of the invention is that the drawbar moving mechanism is relatively compact, especially in the axial direction. The moving mechanism can be arranged in surrounding relation to the drawbar such that it does not increase the axial length of the machine tool. Means are provided for the tool to be self-actuated by using some of the drive power generated from the machine to rotate the tool.
There are in existence various prior art devices associated with rotary spindles for moving a cutter between a extended operating position and a retracted position. U.S. Pat. No. 3,391,585 to Griswold et al shows a double acting hydraulic cylinder for this purpose. U.S. Pat. No. 3,740,161 to V. Milewski also shows a double-acting hydraulic cylinder for retracting a cutter element. U.S. Pat. No. 4,742,738 to K. Strand shows a planetary gearing mechanism for retracting a cutter element carried on a rotary spindle. The use of a harmonic drive means for retracting a rotary cutter element is believed to be new in the art.